I'm trying to change the colour of a label in a WinApi window I'm making. I take hwndConnection, from CreateWindowW() in the WM_CREATE part of my switch statement, and try to pass it to hdcConnection() in the WM_CTLCOLORSTATIC part of my statement.
The problem is that hwndConnection is uninitialised, since it can't be passed from switch statement to switch statement. I'm therefore at a loss at how I should send it between the two.
I tried googling the answer. I found this, which didn't really help me. The accepted answer suggested moving CreateWindowW() out of WM_CREATE (which is how I interpreted it anyway), which causes no compiler errors, but instead a frozen screen. The second uses classes, and some weird syntax I've never seen before (I openly admit I don't know C++).
Here is a stripped down version of my code (I've only included WndProc to keep it consise, however I can include the rest if needed)
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg,
WPARAM wParam, LPARAM lParam) {
HWND hwndConnection;
HDC hdcConnection;
switch (msg) {
case WM_CREATE:
hwndConnection = CreateWindowW(L"Static", L"Not Connected", WS_CHILD | WS_VISIBLE | SS_LEFT, 260, 0, 100, 20, hwnd, (HMENU)1, NULL, NULL);
break;
case WM_CTLCOLORSTATIC:
hdcConnection = GetDC(hwndConnection); // Uninitialised local variable 'hwndConnection' used
SetBkColor(hdcConnection, RGB(255, 0, 0));
return (LRESULT)GetStockObject(NULL_BRUSH);
break;
case WM_COMMAND:
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
}
return DefWindowProcW(hwnd, msg, wParam, lParam);
}
Another way is to declare hwndConnection static:
static HWND hwndConnection(NULL);
If you are paranoid, you may want to check in your case WM_CTLCOLORSTATIC: if it was already set. However, I don't see how you can get WM_CTLCOLORSTATIC before WM_CREATE...
This code works for me:
case WM_CTLCOLORSTATIC:
if ((HWND)lParam == hwndConnection)
{
HDC hdcStatic = (HDC)wParam;
SetBkColor(hdcStatic, RGB(255, 0, 0));
return (LRESULT)GetStockObject(NULL_BRUSH);
}
break;
Your problem is that even if you move hWndConnection out of the switch so that it is in scope for both case branches, it is only initialized in the WM_CREATE branch (and WM_CTLCOLORSTATIC is only taken in a completely different call to the window procedure). However, you can use the GetDlgItem() function to get the handle of a child window, in this case:
case WM_CTLCOLORSTATIC:
hWndConnection = GetDlgItem(hWnd, 1); // 1 is the ID that was assigned as part of the CreateWindow call
hdc = GetDC(hWndConnection);
...
ReleaseDC(hdc);
break;
I want to create a window with CreateWindow() when clicking on a menu item that will be a child of the main window. I know I can use DialogBox() or CreateDialog() but I want to use CreateWindow(). I'm using this code
resource.rc file
#include "resource.h"
IDM_MENU MENU
{
POPUP "&Help"
{
MENUITEM "&About", IDM_HELP
}
}
About window procedure
LRESULT CALLBACK AboutProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
switch(msg)
{
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hwnd, msg, wParam, lParam);
}
return 0;
}
Main window procedure
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
switch(msg)
{
case WM_COMMAND:
switch(LOWORD(wParam))
{
case IDM_HELP:
{
WNDCLASSEX wc;
HWND hDlg;
MSG msg;
SecureZeroMemory(&wc, sizeof(WNDCLASSEX));
wc.cbSize = sizeof(WNDCLASSEX);
wc.hbrBackground = (HBRUSH)(COLOR_BTNFACE+1);
wc.hCursor = LoadCursor(0, IDC_ARROW);
wc.hIcon = (HICON)GetClassLong(hwnd, GCL_HICON);
wc.hIconSm = (HICON)GetClassLong(hwnd, GCL_HICONSM);
wc.hInstance = GetModuleHandle(0);
wc.lpfnWndProc = AboutProc;
wc.lpszClassName = TEXT("AboutClass");
if(!RegisterClassEx(&wc))
break;
hDlg = CreateWindowEx(0, wc.lpszClassName, TEXT("About"), WS_OVERLAPPEDWINDOW, 0, 0, 300, 200, hwnd, 0, wc.hInstance, 0);
ShowWindow(hDlg, SW_SHOWNORMAL);
while(GetMessage(&msg, 0, 0, 0) > 0)
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
UnregisterClass(wc.lpszClassName, wc.hInstance);
}
break;
}
break;
default:
return DefWindowProc(hwnd, msg, wParam, lParam);
}
return 0;
}
Is this a good idea? Can you register more than one class to the same instance? Also, is it a good idea to assign the main window icons to this child window or should I load them each time? Will those icons be deleted when I call UnregisterClass() in IDM_HELP? I have tried this program and everything works and the icons still show in the main window after I close this child window. But I still wonder if it's ok to assign the main window icons to this window since I call UnregisterClass() after the child window closes
There is nothing wrong with using CreateWindow/Ex() instead of CreateDialog()/DialogBox(). And there is nothing wrong with running your own modal message loop, as long as you implement it correctly. For instance, take heed of this warning:
Modality, part 3: The WM_QUIT message
The other important thing about modality is that a WM_QUIT message always breaks the modal loop. Remember this in your own modal loops! If ever you call the PeekMessage function or the GetMessage function and get a WM_QUIT message, you must not only exit your modal loop, but you must also re-generate the WM_QUIT message (via the PostQuitMessage message) so the next outer layer will see the WM_QUIT message and do its cleanup as well. If you fail to propagate the message, the next outer layer will not know that it needs to quit, and the program will seem to "get stuck" in its shutdown code, forcing the user to terminate the process the hard way.
The example you showed is not doing that, so you would need to add it:
ShowWindow(hDlg, SW_SHOWNORMAL);
do
{
BOOL bRet = GetMessage(&msg, 0, 0, 0);
if (bRet > 0)
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
else
{
if (bRet == 0)
PostQuitMessage(msg.wParam); // <-- add this!
break;
}
}
while (1);
UnregisterClass(wc.lpszClassName, wc.hInstance);
However, your modal window should NOT be using WM_QUIT just to break its modal loop, as doing so would exit you entire application! Use a different signal to make your modal loop break when the window is closed. For example:
ShowWindow(hDlg, SW_SHOWNORMAL);
while (IsWindow(hDlg) && (GetMessage(&msg, 0, 0, 0) > 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
LRESULT CALLBACK AboutProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
switch(msg)
{
case WM_CLOSE:
DestroyWindow(hwnd);
break;
default:
return DefWindowProc(hwnd, msg, wParam, lParam);
}
return 0;
}
Also, a modal window is supposed to disable its owner window, and then re-enable it when closed. Your example is not doing that either, so that needs to be added as well:
ShowWindow(hDlg, SW_SHOWNORMAL);
EnableWindow(hwnd, FALSE); // <-- add this
...
LRESULT CALLBACK AboutProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
switch(msg)
{
case WM_CLOSE:
EnableWindow(GetWindow(hwnd, GW_OWNER), TRUE); // <-- add this
DestroyWindow(hwnd);
break;
default:
return DefWindowProc(hwnd, msg, wParam, lParam);
}
return 0;
}
The Old New Thing blog has a whole series of posts on how to work with modal windows.
Modality, part 1: UI-modality vs code-modality
Modality, part 2: Code-modality vs UI-modality
Modality, part 3: The WM_QUIT message
Modality, part 4: The importance of setting the correct owner for modal UI
Modality, part 5: Setting the correct owner for modal UI
Modality, part 6: Interacting with a program that has gone modal
Modality, part 7: A timed MessageBox, the cheap version
Modality, part 8: A timed MessageBox, the better version
Modality, part 9: Setting the correct owner for modal UI, practical exam
The correct order for disabling and enabling windows
Make sure you disable the correct window for modal UI
Update: based on your comment that "No I don't want a modal window", you can ignore everything said above. All of that applies to modal windows only. Since you do not want a modal window, simply remove the secondary loop altogether and let the main message loop handle everything. Also, you do not need to call UnregisterClass(). It will unregister automatically when the process ends. Call RegisterClass() one time, either at program startup, or at least the first time you display the About window. You can use GetClassInfo/Ex() to know whether the class is already registered, or keep track of it yourself. Think of what happens if the user wants to display the About window more than one time during the process's lifetime. So let it re-use an existing class registration each time.
Try this:
LRESULT CALLBACK AboutProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
switch(msg)
{
case WM_CLOSE:
DestroyWindow(hwnd);
break;
default:
return DefWindowProc(hwnd, msg, wParam, lParam);
}
return 0;
}
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
switch(msg)
{
case WM_COMMAND:
switch(LOWORD(wParam))
{
case IDM_HELP:
{
WNDCLASSEX wc = {0};
wc.cbSize = sizeof(WNDCLASSEX);
wc.hInstance = GetModuleHandle(0);
wc.lpszClassName = TEXT("AboutClass");
if (!GetClassInfoEx(wc.hInstance, wc.lpszClassName, &wc))
{
wc.hbrBackground = (HBRUSH)(COLOR_BTNFACE+1);
wc.hCursor = LoadCursor(0, IDC_ARROW);
wc.hIcon = (HICON)GetClassLong(hwnd, GCL_HICON);
wc.hIconSm = (HICON)GetClassLong(hwnd, GCL_HICONSM);
wc.lpfnWndProc = AboutProc;
if (!RegisterClassEx(&wc))
break;
}
HWND hDlg = CreateWindowEx(0, wc.lpszClassName, TEXT("About"), WS_OVERLAPPEDWINDOW, 0, 0, 300, 200, hwnd, 0, wc.hInstance, 0);
if (hDlg)
ShowWindow(hDlg, SW_SHOWNORMAL);
}
break;
}
break;
default:
return DefWindowProc(hwnd, msg, wParam, lParam);
}
return 0;
}
Yes, you can use CreateWindow(). You can do anything in your event handler. Using DialogBox() just gives you a modal loop for free (so your main window cannot be interacted with until the dialog box is closed).
Yes, you can register multiple window classes. You are free to register all your window classes in advance; you do not need to call RegisterClass() and UnregisterClass() each time someone clicks your menu item.
I'm not sure if UnregisterClass() frees the various GDI resources allocated to your window class; anyone who knows the answer is free to comment.
How to write a C Code in order to disable the 'Close Window' option in the taskbar?
Compiler: GCC-mingw32
Which API Function should I use?
Thanks.
Make the window's message dispatcher process the message WM_SYSCOMMAND and filter it out if the message's wParam is SC_CLOSE.
Let WndProc be the windows message handler then the code to do might look like this:
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
...
switch (message)
{
case WM_SYSCOMMAND:
if (wParam == SC_CLOSE);
break;
return DefWindowProc(hWnd, message, wParam, lParam);
case ...
}
return 0;
}
This does not remove the "close"-menu item from the application's jump-list (its taskbar's local menu), but disables its functionality.
I need help with this code. I need to set the focus to a edit button and read the value entered in the edit box and move it to a variable for further processing. This code creates a text prompt with TextOut() which says " Enter the value of mass:" and an editbox with an IDC_EDIT_MASS and hEditMASS next to it.
I am not able to read the value from edit box into variable mass.
And the code is as follows *
#define IDC_EDIT_MASS 103 // Edit box identifier
RESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM
lParam)
{
HWND hEditMASS;
HDC hDC;
PAINTSTRUCT Ps;
HFONT font;
float mass;
char msgMASS[]="Enter the value of mass:";
switch (message) /* handle the messages */
{
case WM_CREATE :
hEditMASS=CreateWindowEx(WS_EX_CLIENTEDGE, “EDIT",
"", WS_CHILD|WS_VISIBLE|ES_MULTILINE|ES_AUTOVSCROLL|ES_AUTOHSCROLL,
550,
200,
200,
20,
hwnd,
(HMENU)IDC_EDIT_MASS,
GetModuleHandle(NULL),
NULL);
Break;
case WM_COMMAND:
switch (LOWORD(wParam)) {
case IDC_EDIT_MASS:
SendMessage(hEditMASS,WM_GETTEXT, sizeof(buffer)/sizeof(buffer[0]),
reinterpret_cast<LPARAM>(buffer));
int ctxtlen=GetWindowTextlength(GetDlgItem(hwnd, IDC_EDIT_MASS));
GetWindowText(GetDlgItem(hwnd, IDC_EDIT_MASS), buffer,(cTxtLen + 1);
mass=atoi(buffer);
MessageBox(NULL,buffer,"Information",MB_ICONINFORMATION);
break;
}
Break;
case WM_SETFOCUS :
SetFocus (hwnd) ;
break;
case WM_PAINT:
hDC = BeginPaint(hwnd, &Ps);
//inputs prompts ...
TextOut(hDC,300,200,msgMASS,sizeof(msgMASS));
EndPaint(hwnd, &Ps);
break;
case WM_DESTROY:
PostQuitMessage (0); /* send a WM_QUIT to the message queue */
break;
default: /* for messages that we don't deal with */
return DefWindowProc (hwnd, message, wParam, lParam);
}
return 0;
}
hEditMASS is an local, automatic-storage-duration variable. You set it when the message is WM_CREATE. However, you then access it when the message is WM_COMMAND. Automatic-storage-duration variables do not retain their value between calls. In order for it to retain its value, you must either make it global or make it static, e.g.:
static HWND hEditMASS;
Keep in mind that you'll probably only be able to use your window procedure for one window now, since creating any other window with the same window procedure will end up using the same hEditMASS variable, and when you next try to access hEditMASS, it will point to the edit control in the most-recently-created window with that window procedure.
I want to trap keyboard messages in a console application, so I tried this:
HWND GetConsoleHwnd(void)
{
#define SIZEBUF 1024
char szBuffer[SIZEBUF];
GetConsoleTitle(szBuffer, SIZEBUF);
#undef SIZEBUF
return FindWindow(NULL, szBuffer);
}
LRESULT CALLBACK ConsoleProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
switch (msg)
{
case WM_KEYDOWN:
switch (wParam)
{
//VK Cases
}
break;
}
return CallWindowProc(OldConsoleProc, hwnd, msg, wParam, lParam);
}
this in main:
HWND hwndConsole = GetConsoleHwnd();
OldConsoleProc = (WNDPROC) SetWindowLong(hwndConsole, GWL_WNDPROC,
ConsoleProc);
and this Global Var: WNDPROC OldConsoleProc;
but it doesnt work, what I am doing wrong?
You can't subclass a window of another process this way. You can do it with hooks but I wouldn't recommend trying this on console window. ReadConsoleInput is low-level enough, and it's as far as you can get without ugly nonportable hacks (I'm not even sure there are some events reaching WndProc when the console window is full screen).